Miniaturized Air-to-Refrigerant Heat Exchangers 2016 Building Technologies Office Peer Review 20%+ Better Reinhard Radermacher [email protected] University of Maryland College Park Project Summary Timeline: Key Partners: Start date: 3/1/2013 Oak Ridge National Original end date: 2/29/2016 Laboratory Revised end date: 10/30/2016 Burr Oak Tool Heat Transfer Technologies Key Milestones International Copper 1. Design optimization, 3/30/14 Association 2. Fabrication/testing, 1kW prototype, 6/30/2015 Luvata 3. Fabrication/testing, 10kW prototype, 1/30/2016 Wieland Project Goal: Budget: Purpose: Develop next generation heat Total Budget: $1500K exchangers for heat pumps and air-conditioners Target Performance: Miniaturized air-to- Total UMD: $1050K refrigerant heat exchangers with at least Total DOE $ to date for UMD: $1050K • 20% lower volume • 20% less material • 20% higher performance Target Market/Audience: Target Market: To be in production within five Residential and commercial heat pump years systems with various capacity scales. Condenser as first choice of application 2 Purpose and Objectives Problem Statement: Develop miniaturized air-to-refrigerant heat exchangers that are 20% better, in size, weight and performance, than current designs AND In production within 5 Years Target Market and Audience: . Residential and commercial heat pumps and air-conditioners . US Shipment of residential air-source equipment in 2011: 5.5 Million units . US EIA 2009 Energy Consumption: 41.5% for space heating, 6.2% for AC . Proposed heat exchanger technology will readily compete with current condenser designs for AC systems (3.7 M). Impact of Project: . Project deliverables include analyses tools and heat transfer correlations . Heat exchangers (1 kW and 10 kW) that are at-least 20% better (size, weight and performance) than current designs, based on measured performance; a minimum of 3 prototypes to be fabricated and tested . Manufacturing guidelines to facilitate production within 5 years 3 Future of Heat Exchangers 4 Approach . Developed a comprehensive multi-scale modeling and optimization approach for design optimization of novel heat exchangers • Parallel Parameterized CFD • Approximation Assisted Optimization . Build a test facility for air side performance measurement of heat exchangers . Design, optimize and test 1 kW and 10 kW air-to-water and air-to- refrigerant heat exchangers . Investigate conventional and additive manufacturing techniques . Analyze and test system level performance of novel heat exchangers • Evaporator and condenser of a system based on same design 5 Approach : Key Issues . Lack of basic heat transfer and fluid flow data for design and analyses of air-to-refrigerant heat exchangers with small flow channels . Availability for small diameter tubes and manufacturing quality control . Joining/manufacturing challenges . Face area constraints . Fouling and flow mal-distribution . Wetting . Noise and vibrations 6 Approach: Distinctive Characteristics . Developed a comprehensive multi-scale modeling and optimization approach for design optimization of novel heat exchangers • Allows for rapid and automated CFD evaluation of geometries with shape and topology change • More than 90% reduction in engineering and computation time . Focus on small hydraulic diameter flow channels • Bridging the research gaps • Heat transfer, pressure drop correlations and design tools . Prototype fabrication and testing is in progress, with target production within 5 years . Initial tests show, <10% deviation compared to predicted values . 20% size and weight reduction . Retrofit applications, limited load carrying capacity of roofs . Potential savings in logistics costs 7 Progress and Accomplishments . Analyzed 15+ heat exchanger geometries . Developed a new methodology for optimizing tube shapes – no longer constrained by circular/rectangular tubes . Fabricated and tested three 1kW prototypes • Measured data for dry tests agree within 10% of predicted performance for heat transfer and 20% for pressure drop • Wet tests show significant pressure drop penalty . Fabricated and tested one 10kW radiator . Challenges with tube blockage . Work in progress • Fabrication of 3TR evaporator and condenser • System-test facility is developed, equipment donated by sponsors of UMD-CEEE Consortium 8 Accomplishments Fixed flow rates; ΔT=50K(MCHX / NGHX13); ΔT=42K (BTHX / FTHX); ΔT=40K (NTHX) MCHXMCHXMCHX (Baseline) (Baseline)(Baseline) FTHXFTHX Prototype 2 NGHX13NGHX13 (NTHX) NTHX BTHXBTHX 0.8mm0.8mm Prototype 1 MCHX (Optimized) (BTHX) MCHXMCHXMCHX (Optimized)(Optimized)(Optimized) BTHXBTHX 0.5mm0.5mm Finned Web-Tube Round Bare Tubes Plain Fin-Tube NURBS-based Face Microchannel (NGHX13) (BTHX) (FTHX) Tube Area (cm²) (MCHX) (NTHX) 100 400 9 Accomplishments (non-Animated) Fixed flow rates; ΔT=50K(MCHX / NGHX13); ΔT=42K (BTHX / FTHX); ΔT=40K (NTHX) MCHX (Baseline) FTHX Prototype 2 NGHX13 (NTHX) NTHX BTHX 0.8mm Prototype 1 (BTHX) MCHX (Optimized) BTHX 0.5mm Finned Web-Tube Round Bare Tubes Plain Fin-Tube NURBS-based Face Microchannel (NGHX13) (BTHX) (FTHX) Tube Area (cm²) (MCHX) (NTHX) 100 400 10 Progress and Accomplishments . Novel multi-scale approach for tube shape optimization 100 mm 100 mm 11 18 mm Accomplishments: Causes for Deviation: Round Bare NURBS-based Air-by pass; Measurement Tubes Tube uncertainty; Un-even tube spacing (RTHX) (NTHX) 12 Accomplishments: Wet Tests (Vertical Orientation) 1.1 350 Dry, MFR_w=20 g/s 1.0 Dry, MFR_w=35 g/s 300 Dry, MFR_w=50 g/s 0.9 RH=51%, MFR_w=20 g/s RH=51%, MFR_w=35 g/s 0.8 ] 250 RH=51%, MFR_w=50 g/s RH=70%, MFR_w=20 g/s 0.7 RH=70%, MFR_w=35 g/s 0.6 200 RH=70%, MFR_w=50 g/s 0.5 150 0.4 Sensible ratio heat 0.3 RH=51%, MFR_w=20 g/s Air pressure drop [Pa 100 RH=51%, MFR_w=35 g/s 0.2 RH=51%, MFR_w=50 g/s RH=70%, MFR_w=20 g/s 50 0.1 RH=70%, MFR_w=35 g/s RH=70%, MFR_w=50 g/s 0.0 0 0 1 2 3 4 5 0 1 2 3 4 5 Air velocity [m/s] Air velocity [m/s] 13 Accomplishments: Wet Tests, Horizontal vs. Vertical 1400 1400 Dry, MFR_w=20 g/s Dry, MFR_w=20 g/s Dry, MFR_w=35 g/s Dry, MFR_w=35 g/s 1200 Dry, MFR_w=50 g/s 1200 Dry, MFR_w=50 g/s RH=51%, MFR_w=20 g/s RH=51%, MFR_w=20 g/s RH=51%, MFR_w=35 g/s ] 1000 RH=51%, MFR_w=35 g/s 1000 ] RH=51%, MFR_w=50 g/s RH=51%, MFR_w=50 g/s RH=70%, MFR_w=20 g/s RH=70%, MFR_w=20 g/s RH=70%, MFR_w=35 g/s 800 RH=70%, MFR_w=35 g/s 800 RH=70%, MFR_w=50 g/s RH=70%, MFR_w=50 g/s 600 600 Capacity for vertical [W vertical for Capacity Capacity for horizontal [W horizontal for Capacity 400 400 200 200 0 0 0 1 2 3 4 5 0 1 2 3 4 5 Air velocity [m/s] Air velocity [m/s] 14 Accomplishments: 10kW Radiator Fabrication 1kW: 484 Tubes, 140mm x 150mm 10kW: 2280 Tubes, 444mm x 580mm Tube Defects Significant tubes had fractures and leaks Had to re-order entire batch of tubes from a different vendor 15 Accomplishments: Process Improvement • Separate soldering process improves control and reduces complexity; New method – solder tube to header separately • Header to manifold soldering without an oven provides cleaner appearance and allows any size HX to be made 16 Accomplishments: 10kW Radiator Tests • ~25% tubes blocked in end rows • Needs further investigation 17 Lessons Learned from Fabrication and Testing • Quality control during manufacturing of small diameter tubes is critical • Heat exchanger core needs to be flushed/cleaned before final manifold soldering; conduct single manifold flow tests – Material reactions could also cause blockages • Uncertainty in latent heat load dominated by the uncertainty in humidity measurement. ASHRAE standard requirements do not guarantee 5% uncertainty for all test conditions • Under dry conditions, the orientation of heat exchanger has no measurable impact on capacity. Under wet conditions, horizontal orientation has lower capacity than vertical orientation. • Significant bridging effect of condensate water for bare tube heat exchangers is observed. The pressure drop penalty under wet conditions is much higher than traditional heat exchangers. – Need to use coatings. 18 3TR Evaporator and Condenser Designs • Geometries: Round bare tubes, inline and staggered • 3ton heat pump unit 1.10 COP Charge Indoor Unit Outdoor Unit (Cooling) (Cooling) 1.05 = ∆ min fp1 = ∆ air min fp1 air = 1.00 min fV2 = HX min fV2 HX st.. st.. 10.5≤≤Q& 11.0 kW 13.0≤≤Q& 13.5 kW 0.95 ∆pp ≤0.8 ⋅∆ ∆ppair ≤0.8 ⋅∆ air_ baseline air air_ baseline Values Normalized ≤⋅ 0.90 VVHX ≤⋅0.5 baseline VVHX 0.5 baseline 0.2≤≤AR 1.0 uair ≤1.2 m/s lm≤ 0.5 0.85 Baseline Opt1 Opt2 Cycle Opt1 and Opt2 are two optimized designs 19 Accomplishments: Design Tools for Industry Round Bare Tube HX . Air-side heat transfer and pressure drop correlations Plain Fin Tube HX Wavy Fin Tube HX 20 Project Integration and Collaboration Project Integration . Collaboration with key project partners to identify and solve manufacturing and deployment challenges . Collaboration with ORNL for performance testing and advanced manufacturing . First-hand feedback from industry partners of UMD Consortium Partners, Subcontractors, and Collaborators . ORNL: Subcontractor; design, advanced manufacturing and testing • Omar Abdelaziz: Group Leader, PI; Patrick Geoghegan: Scientist . Luvata: Industry partner; manufacturing, system integration and marketing • Mike Heidenreich: VP of Product Engg; Russ Cude: Director of Engg., Americans; Randy Weaver: R&D Engineer . ICA / Heat Transfer Technologies: Industry partner; heat exchanger manufacturing process development • Yoram Shabtay: President; John Black: VP of Market Development . Wieland: Industry Partner; tube manufacturer . Steffen Rieger, Technical Marketing Manager . Burr Oak Tool Inc.: Specializing in machines, tools and services for HX mfg. Roger Tetzloff, Innovations Manager 21 Project Communications Progress Review Meetings: • Kick-off Meeting & Brainstorming Workshop, 22-Apr-2013, University of Maryland • Semi-annual in-person progress review meetings (Mar and Sep), every year IP: Invention records and provisional patent application in progress Total Publications: 2014- 4, 2015- 3, 2016- 1, and 6 drafting Selected Publications 1.